Comment by mcpherrinm

It doesn't matter what the network is doing; the phone needs to disable 2g. There's various ways to get the phone to downgrade to 2g otherwise, eg https://montsecure.com/files/2021_downgrade.pdf

Android has it as a toggle: https://source.android.com/docs/security/features/cellular-s...

iPhone disables it for phones in lockdown mode.